Questions about using a timing light

[dmjlambert]

Hi, I have a question about a timing light, please. I bought the fancier of the two Bosch lights offered at O'Reilly. I am not trying to set the timing right now, just observe what my timing is set to, and learn some. I have a 1969 CST/10 with 350 engine and quadrajet, and it has an HEI distributor from a later model year. My vacuum advance is connected to a manifold vacuum port on the carburetor (has vacuum at idle) during my observations.

I connected the timing light and it is set it for 4 cycle by default when turned on. I start the engine.

I point the light to the timing marks and pressed advance up button on the light until the mark on the balancer aligned with the 0 mark on the timing tag. The timing light reads 30.0. Then I continue to adjust the advance up button until the mark on the balancer lines up 5 marks to the right near the R. The timing light new reads 40.0.

Does each mark on the timing tag represent 1 degree? I do not have the type of timing tag with notches, the edge is flat as shown in the picture.

When I set the timing light to 2 cycle, the reading is 15.0 when the mark on the balancer aligned with the 0 mark on the timing tag, and the reading is 20.0 when lines up with 5 marks to the right near the R. So I am thinking 2 cycle setting is the appropriate one to use with this timing light and this engine, and I have 15 degrees total advance at idle. Do I understand this correctly?